1. Field of the Invention
The field of invention relates to a method and apparatus for treating a formation. More specifically, the field relates to a method and apparatus for isolating and selectively treating a hydrocarbon-bearing stratum.
2. Description of the Related Art
It is common in petroleum recovery to inject treatment chemicals into a well bore or into a subterranean formation in order to change its physical properties, including increasing permeability, removal of mineral or organic scales, reducing permeability to decrease water influx, and altering water production distribution along the length of the well bore.
An example of injecting a treatment chemical includes introducing an acidic fluid onto a well bore wall. The acidization treatment is performed to increase the permeability of the surrounding hydrocarbon-bearing stratum and facilitate the flow of hydrocarbons into the well from the face of the formation. In matrix acidizing, the acid-bearing fluid passes into the formation at a pressure less than the fracturing pressure of the hydrocarbon-bearing stratum. Increased permeability is obtained through chemical reaction between the acidic fluid and the hydrocarbon-bearing stratum, not by “fracking” the hydrocarbon-bearing stratum through over pressurization of the introduced fluid.
Another example of injecting a treatment chemical includes “acid fracking” of a carbonate formation. Acidic fluids are introduced into the well bore at pressures and fluid velocities sufficient to exceed the fracture gradient of the treated stratum. The effect is to physically fracture the rock within the hydrocarbon-bearing stratum while also chemically etching the exposed faces along the new fracture lines. The combination of fracking and acid etching forms new flow channels in the formation for either hydrocarbon-bearing fluid production or additional treatment injections.
As previously suggested, both matrix and fracture acid injection are only two of several ways to enhance, control and modify the productivity or injectivity, or both, of a formation. Other chemical treatments include well-bore clean-up, drilling damage removal, water conformance and shut-off, relative permeability modifiers (RPM) fluids, proppant fracking, jetting, mineral and organic scale mitigation and removal, and chemical, scale and corrosion control squeezes.
An important factor in ensuring the efficacy of any chemical treatment is the chemical's delivery to the treatment site. The treatment chemical should be introduced preferably in a manner that focuses the treatment chemical only into the area or onto the surface to be treated. This helps ensure that the chemical treatment is at its maximum efficacy upon application.
Application of such chemical treatments currently occur by deploying a tool into a well bore using a coiled tubing unit (CTU) or other tubing conveyed platforms such as a conventional or workover rig. Such a deployment means has several limitations. Such units, even CTUs, are expensive to rent by the hour, and sometimes there are long wait times for availability and transportation issues for remote locations inland. This results in delayed flow-back from the well of production fluid that can be processed by surface units. After placement of the tool by the CTU or rig, a high-pressure surface pump is required to pressurize the treatment chemical for introduction into the tool through the CTU. After applying the treatment chemical at the site, there is usually no means for removing the spent chemical treatment fluid from the application site. “Reversing” the flow path of high-pressure surface pumps requires engineering and construction support not typically found on location, where typically the rigs or units are simply dropped off and erected. Tubing units may not have the proper materials of construction to permit both the application of the treatment chemical and then exposure to the spent treatment chemical by reversing flow. “Lifting” the spent treatment fluid as well as potentially production fluids from the treatment site may resulting in the spent treatment fluid containing rock, sand and other particulates, spent treatment chemical, water, brines and hydrocarbon-bearing fluids from the treated stratum. If any gas is present in the production fluid, its rapid depressurization under surface pumping may cause a loss of well bore control. Finally, the tool must be extracted from the well bore, the well bore fluid balanced for production testing to prevent flow back and the treatment's effectiveness determined through direct or indirect detection means. If the treatment was unsuccessful, all of the equipment for treatment application needs to be reinstalled again.
If a coiled tubing unit is not used to deliver the treatment chemicals to the well bore site, treatment of the targeted stratum may become less expensive but more technically difficult as only differences in fluid properties are used to target the treatment site and preventing the remainder of the well bore from inadvertent treatment. Without a CTU or other fluid delivery means downhole at the treatment site, the chemical treatment must be “bullheaded” (that is, pumped down the producing string or casing) to the targeted stratum. Diversion fluids are often used to route the treatment chemical to the treatment site using physical (for example, density) or chemical (for example, aqueous vs. hydrocarbon incompatibility) differences between the fluids. The placement of diverting fluids is property and condition dependent—minor changes in composition, such as salinity or water content, or temperature, can cause diverting fluids to mix or blend unexpectedly, to be absorbed into the formation, to invert and change positions within the well bore, to react prematurely or to not react at all.
If diversion fluids are not used, the treatment chemical can be introduced from the surface and mixed with the entirety of the well bore fluid using low pressure well bore fluid circulation pumps. These low pressure circulation pumps are standard equipment on rigs that drill into formations and form well bores. However, this is not a desirable option if the treatment chemical is active on other constituents within the well bore or with constituents of the well bore fluid, including casing, exposed well bore walls, equipment and prior treatments sites. Bullheading such a treatment chemical often requires a greater volume of chemicals as the efficacy of the treatment chemical is diluted due to blending, fluid friction, emulsification, reaction with other chemicals, mixing with the well bore fluid.
It is desirable to find an isolation and application apparatus and a method of using the apparatus to apply a treatment chemical to the targeted formation without the need for using coiled tubing or specialized workover units. It is also desirable to be able to easily convey the treatment chemical to the targeted stratum using lower pressure surface pumps while maintaining a high treatment chemical efficacy. It is also desirable to be able to remove the treatment chemical from the application site to evaluate the treatment's efficiency as well as to performance test the treated stratum before removing the isolation and application apparatus.